[A/N: Just some fluffy backstory I wanted to write, basically establishing the friendship between Itachi and Shisui. Written for Timelines, but works with canon, Turning Points, whatever.]
First Meetings:
"Shisui-kun, this is Itachi-chan. You be sure to take good care of him while your Aunt Mikoto is at the hospital with me, ne?"
As the door closed behind his mother, Shisui looked doubtfully down at the younger boy. He had never seen much of Itachi—just the odd glimpse of the clan heir training with his private tutors—but he had heard plenty. It was hard not to, when the three-year-old was reportedly already at a Second-year Academy level. Shisui himself had only entered the Academy last month.
What was he supposed to do with a baby genius, anyway? Itachi looked like a normal enough kid, if more solemn than most boys his age.
"Are you hungry?" Shisui asked experimentally. Itachi shook his head. He didn't look like he knew what he was supposed to be doing, either. "Well, do you want to play a game?"
Itachi stared back blankly. "Game?"
"Don't you know any games?" Shisui asked, horrified.
"I don't have anyone to play with," Itachi replied. Shisui was surprised at how articulate he was, and not a little embarrassed at his own attempts to use simple words. "Besides," Itachi added, "I'm too busy training."
Shisui would have to do something about this. "Don't worry, I'll teach you! I know lots of games. Now, let's see...tag's no fun with only two people, but we could play Hide-and-Find!"
"What's that?"
"That's where one person hides something and the other person has to find it," Shisui explained. "Come on, let's go get something to hide!" He scampered off to his room, Itachi following closely behind. Once there, Shisui selected a stuffed squirrel that was big enough not to get lost in a gap but small enough to be easily hidden. "Now," he instructed, "You wait here while I hide this, and then you try to find it. Okay?"
Itachi nodded, and Shisui ran back into the living room, making sure his bedroom door was closed all the way first.
Of course, Shisui wasn't going to make it easy just because Itachi was three years old. He was a genius, after all. Dragging in one of the tall kitchen stools, he set it up in front of the bookcase. He could just reach the very top while standing on the stool. Carefully, he tucked the squirrel behind a family picture so that it was almost completely hidden. Jumping down from the stool, he surveyed his handiwork with satisfaction. A child of Itachi's height wouldn't be able to see it unless they were almost all the way across the room. Just to make sure Itachi didn't get any hints, Shisui dragged the stool back into the kitchen before running back to the bedroom.
"Okay!" he announced, pushing the door open, "You can come look for it now!"
Itachi promptly jumped off the bed and headed into the living room, Shisui following behind, smiling smugly. Once in the living room, Itachi didn't dash around blindly like most of the kids Shisui played with. Instead, he methodically examined every piece of furniture in the room. Shisui didn't watch, but perched on the back of the couch to wait for Itachi to ask for help; the kid couldn't possibly figure out Shisui's awesome hiding spot!
Luckily, he turned around when he heard a quiet scrambling sound—just in time to see Itachi perched on the top shelf of the bookcase, reaching back to grab the squirrel. "Hey, watch out!" Shisui shouted as Itachi's foot slipped off the shelf. Itachi grabbed for the top of the bookcase as he fell, but missed. Shisui just managed to get under Itachi before he hit the ground, and got all the breath knocked out of him for his pains. The family photo landed beside them, the glass over the picture shattering all over the floor.
"I found the squirrel," Itachi said, smiling for the first time.
"That's great," Shisui gasped.
Itachi frowned. "Shisui-san, are you hurt?"
"No, I'm fine," Shisui lied, as Itachi got off of his rib cage. "Next time ask me to get a stool or something, okay? Come on," he continued as he dragged himself to his feet, "we've got to get this cleaned up before Mom gets back."
With Itachi holding the dustpan and Shisui sweeping, the glass was quickly disposed of. Shisui put the photo frame back up on the bookcase—while his parents would of course find out eventually, he wanted to delay the inevitable as long as possible.
That little interlude now over, they continued playing Hide-and-Find, only for Shisui to find out that Itachi was just as good at hiding as he was at finding. Shisui finally called it quits after seven rounds of being thoroughly trounced.
By now they were both very hungry, so Shisui opened the fridge to see what his mother had left for them to eat. There were two juiceboxes and a plate of onigiri which they split between them.
"Do you want to see the rest of the house?" Shisui asked, after slurping up the last few drops of his juice.
"If you like, Shisui-san," Itachi replied.
Shisui spent the next ten minutes giving his young cousin the grand tour of his ancestral home, including the shed out back, which had tons of super awesome stuff to play with as long as you didn't get caught playing with it.
"Shisui-san, what's in there?" Itachi asked finally, pointing at the one door in the hallway that Shisui hadn't opened.
Shisui made a mental note to tell Itachi to stop calling him 'Shisui-san'. It was totally weird. "It's the room for the new baby," he explained, trying the door. To his surprise, it was unlocked, and he pushed it open a few inches so Itachi could look through.
"There isn't much in there," Itachi said.
"They haven't finished painting yet," Shisui replied. "See, they left all the paint and stuff here." Suddenly, Shisui had a brilliant idea. This should have been a warning in and of itself, considering what had happened the last few times he had had brilliant ideas. "Hey, Itachi," he said, "I just had a brilliant idea."
"Oh?" Itachi looked a bit doubtful, but Shisui decided he could be forgiven for that. He was a baby genius, after all.
"Yeah. See, let's paint the rest of the baby's room before Mom gets back and surprise her!"
"Are you sure that's a good idea, Shisui-san?"
"Of course it is! It's my idea, isn't it?"
Shisui promptly set to work. Itachi was more reluctant but willing to do whatever Shisui asked. Soon, they had painted the remaining walls, as well as themselves. Shisui had more trouble figuring out how they were supposed to paint the ceiling, since he was too short, even when standing on a chair. However, if he stood on the chair, then picked up Itachi, Itachi could just reach the ceiling with his brush. By this point, the two boys were almost as white as the walls, but they didn't really care. Or rather, Shisui didn't care, and told Itachi that he didn't need to care either.
They were almost half done with the ceiling when they heard the front door open. "Shisui-kun! Itachi-chan! We're back!"
"Mom!" Shisui gasped. "She can't see this!"
"But I thought that was the point, Shisui-san?" Itachi said bewilderedly.
"Well, yeah, but not when we're all messy like this. Come on, let's see if we can get you cleaned up before your mom sees."
Shisui opened the door a crack to see if the coast was clear, then ducked into the bathroom across the hall. Itachi was already there. There was really nothing to be done about the paint on Itachi's clothes, but Shisui managed to get most of the paint of his face, at least. He was just about to see if there was any way to get the paint out of his cousin's hair when the bathroom door opened.
"Great nine-tails! What have you been doing?"
Shisui learned three things that day: First, that babysitting was a lot easier than he had thought. Second, that Itachi was surprisingly fun to play with for a baby genius. And third, that Aunt Mikoto could be very, very scary.